using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.EventSystems;
 
public class DragUI_Overlay : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
{
    /// <summary>
    /// UI和指针的位置偏移量
    /// </summary>
    Vector3 offset;
 
    RectTransform rt;
    Vector3 pos;                
    float minWidth;             //水平最小拖拽范围
    float maxWidth ;            //水平最大拖拽范围
    float minHeight;            //垂直最小拖拽范围  
    float maxHeight;            //垂直最大拖拽范围
    float rangeX;               //拖拽范围
    float rangeY;               //拖拽范围
 
 
    void Update()
    {
        DragRangeLimit();
    }
 
    void Start()
    {
        rt = GetComponent<RectTransform>();
        pos = rt.position;
        //Debug.Log(pos);
        minWidth = rt.rect.width / 2;                           
        maxWidth = Screen.width - (rt.rect.width / 2);
        minHeight = rt.rect.height / 2;
        maxHeight = Screen.height - (rt.rect.height / 2);
    }
 
    /// <summary>
    /// 拖拽范围限制
    /// </summary>
    void DragRangeLimit()
    {
        //限制水平/垂直拖拽范围在最小/最大值内
        rangeX = Mathf.Clamp(rt.position.x, minWidth, maxWidth);
        rangeY = Mathf.Clamp(rt.position.y, minHeight, maxHeight);
        //更新位置
        rt.position = new Vector3(rangeX, rangeY, 0);
    }
 
    /// <summary>
    /// 开始拖拽
    /// </summary>
    public void OnBeginDrag(PointerEventData eventData)
    {
        Vector3 globalMousePos;
 
        //将屏幕坐标转换成世界坐标
        if (RectTransformUtility.ScreenPointToWorldPointInRectangle(rt, eventData.position, null, out globalMousePos))
        {
            //计算UI和指针之间的位置偏移量
            offset = rt.position - globalMousePos;
        }
    }
 
    /// <summary>
    /// 拖拽中
    /// </summary>
    public void OnDrag(PointerEventData eventData)
    {
        SetDraggedPosition(eventData);
    }
 
    /// <summary>
    /// 结束拖拽
    /// </summary>
    public void OnEndDrag(PointerEventData eventData)
    {
 
    }
 
    /// <summary>
    /// 更新UI的位置
    /// </summary>
    private void SetDraggedPosition(PointerEventData eventData)
    {
        Vector3 globalMousePos;
 
        if (RectTransformUtility.ScreenPointToWorldPointInRectangle(rt, eventData.position, null, out globalMousePos))
        {
            rt.position = offset + globalMousePos;
        }
    }
}